don't call _tp_contacts_to_handles in g_return_if_fail
don't call _tp_contacts_to_handles in g_return_if_fail

g_return_if_fail() can be compiled as noop, so we shouldn't rely on it to get
the handles.

Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib